Bug #79111 w/ DATE_FORMAT, NULLIF works together, incorrect result is returned

• Submitted: 4 Nov 2015 5:57
• Modified: 4 Nov 2015 6:32
• Reporter: Su Dylan
• Status: Verified
• Category: MySQL Server: DML
• Severity: S3 (Non-critical)
• Version: 5.7.8, 5.6.27, 5.7.9
• OS: Any
• CPU Architecture: Any
• Tags: regression

[4 Nov 2015 5:57] Su Dylan

Description:
Output:
=======
mysql> SELECT date_format(NULLIF('2015-01-01','2015-01-02'), '%Y');
+------------------------------------------------------+
| date_format(NULLIF('2015-01-01','2015-01-02'), '%Y') |
+------------------------------------------------------+
| NULL                                                 |
+------------------------------------------------------+
1 row in set, 2 warnings (0.00 sec)

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.8-rc  |
+-----------+
1 row in set (0.00 sec)

Problem:
========
'2015' is expected.

How to repeat:
SELECT date_format(NULLIF('2015-01-01','2015-01-02'), '%Y');

Suggested fix:
'2015' is returned.

[4 Nov 2015 6:32] MySQL Verification Team

Hello Su Dylan,

Thank you for the report and test case.

Thanks,
Umesh